Orthosilicate alkaline flooding

Alkaline flooding is also called caustic flooding. Alkalis used for in situ formation of surfactants include sodium hydroxide, sodium carbonate, sodium orthosilicate, sodium tripolyphosphate, sodium metaborate, ammonium hydroxide, and ammonium carbonate. In the past, the first two were used most often. However, owing to the emulsion and scaling problems observed in Chinese field applications, the tendency now is not to use sodium hydroxide. The dissociation of an alkali results in high pH. For example, NaOH dissociates to yield OH" ... 

A number of laboratory investigations were made into different aspects of consumption of sodium hydroxide and sodium orthosilicate in alkaline flooding of petroleum reservoirs for enhanced oil recovery. One investigation studied the role of reversible adsorption and of chemical reaction v en petroleum reservoir sands are contacted with alkaline solutiais. Another investigation studied the effect of flow rate on caustic consumption by means of a series of flow experiments through reservoir sand packs. A third series of high rate flow experiments studied changing alkaline consumption with time. 

In comparing sodium hydroxide and sodium orthosilicate solutions of the same concentration the alkaline consumption for sodium orthosilicate was significantly lower than that for sodium hydroxide. For example, the alkaline consumption of TRIMS Ranger sand was 9.2 mec lOOg sand for 1.0% sodium orthosilicate vhile the consumption was 25.1 meq/lOOg for 1.0% sodium hydroxide. Thus sodiuti orthosilicate seems to be superior to sodium hydroxide for alkaline flooding. 

The chemicals which have been used, or are being used, for alkaline flooding are sodium orthosilicate and sodium hydroxide. Sodium carbonate and sodium tripolyphosphate are not alkaline enough to react with the acids in crude oils. Johnson (6) and Mungan (9) have published reviews of alkaline flooding in which they summarize the proposed mechanisms of oil displacement (Table 2) and some of the important parameters for selection of alkaline flooding candidates (Table 3). These topics are covered in these two publications and will not be discussed further in this paper. 

The data from these tests show that sodium orthosilicate is more effective than sodium hydroxide in recovering residual oil under the conditions studied, both for continuous flooding and when 0.5 PV of alkali was injected. The mechanisms through which sodium orthosilicate produced better recovery than sodium hydroxide in this system have not been completely elucidated. Reduction in interfacial tension is similar for both chemicals, so other factors must play a more important role. Somasundaran (26) has shown that sodium silicates are more effective than other alkaline chemicals in reducing surfactant adsorption on rock surfaces. Wasan (27,28) has indicated that there are differences in coalescence behavior and emulsion stability which favor sodium orthosilicate over sodium hydroxide. Further work is being done in this area in an attempt to define the limits of physically measurable parameters which can be used for screening potential alkaline flooding candidates. 

Work by Holm (14, 15) has established the benefit of using alkaline chemicals as a preflush agent for micellar/polymer floods. A field trial of this process using an orthosilicate preflush has been carried out at Gary Energy s Bell Creek Field... 

A number of different alkaline agents, e.g., sodium hydroxide, sodium carbonate, sodium orthosilicate, ammonium hydroxide, etc., have been considered and added to flood-waters throughout the world, since the early 1900 In... 

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